Photodetectors comprise layers of photosensitive materials that can detect incident light of certain photon energies (which may also be expressed as wavelengths) related to the bandgap of the material. A bandgap is defined as the gap, expressed as an energy, between the lowest point of the conduction band and the highest point of the valence band of the material's electron energy dispersion relation (E-k) diagram, an example of which is shown as FIG. 1. Absorption of photons having at least the bandgap energy excites electrons from the valence band energy to the conduction band energy, thereby producing a photocurrent which can then be measured.
In existing photodetector technology, various materials having different bandgaps are used to detect different spectral ranges of incident electromagnetic radiation. However, the bandgaps, and thus the detectable range of photon energies, are fixed for the materials that are used in the device. This presents a profound limitation of the usefulness of the photodetector device.